Protestantism was a big part of the turn towards individualism, I think. But the Christian duplicity I have in mind isn’t the same as individualism. I think it’s better characterized as Catholicism in the strict sense of being a universalizing, all-things-to-all people strategy found throughout Christian history. This is syncretism on steroids, an eclectic borrowing and compromising in the service of evangelism, the purpose being the world’s conversion to Christianity even at the cost of the religion’s coherence, original message, and spiritual power.
The Christian emphasis on faith rather than works doesn’t really entail individualism or Protestantism, since creedalism could just as easily be compatible with group-think. Luther was the first who took that emphasis in a solipsistic and individualistic direction.